OENERAL MORPHOLOGY OF FUNGI 



21 



develops on a fructification whose structure is highly differentiated. In the 

 higher groups, the fructifications containing the gonotoconts become visible 

 to the naked eye and are called the perfect forms. The other spore forms are 

 referred to as imperfect or secondary spore forms. 



Sexual Organs and Sexuality. — The sexual function in its simplest stage 

 involves but two processes : (a) fertilization, a fusion of two nuclei, recurring 

 periodically in the course of development, initiating specific stimuli for fur- 

 ther development; and (b) meiosis, a return to the single chromosome num- 

 ber. This rotation (haplont -^ fertilization — > diplont -^ meiosis — >) comprises 

 the changes of nuclear condition in most organisms. A few fungi seem to 

 exist without such a change; they seem to live an unlimited number of "gen- 

 erations" without reconstruction of their nuclei and to propagate themselves 



Fig-. 3. — Coremium. Hemispora coremiformis. (After M. Moore 1935.) 



by imperfect stages only. Such fungi with incomplete, or incompletely known 

 life cycles are called Fungi Imperfecti. 



The fungi with complete life cycles are divided into homothallic (her- 

 maphroditic) and heterothallic forms. In contrast to the higher plants and 

 animals, the division of sexes is here limited to the haplont, i.e., the mycelium. 

 The homothallic form is often indicated by the symbol ±, the heterothallic 

 forms as + or -. The + and - mycelia of the latter group may be distinguished 

 from each other only physiologically, as indicated by their sexual tendencies, 

 or morphologically as well (e.g., in growth form, sexual dimorphism). 



Fertilization in fungi, as in protozoa, may occur in many ways. The 

 simplest normal type of fertilization, when two spatially separated, not closely 

 related sexual cells fuse to form a new entity, is called amphimixis. 



If the sexual cells arise as daughter cells of a differentiated mother cell 

 and are themselves characteristically formed, they are called gametes and 



